l8o THE ELECTRIC ARC 



the electrodes. There is no question but that such action 

 at the cathode makes it easier for the current to flow, 

 as has already been shown, but the experiments of Weedon 

 show that this is not essential. 



There has been some discussion as to whether the current 

 is carried by the vapors which come from the anode or by 

 those coming from the cathode. Steinmetz 1 says that it is 

 carried by a blast from the cathode. Blondel 2 believes that 

 it is carried by material coming from the anode. It would 

 seem that neither of these views is entirely correct. The 

 current is carried by that part of the vapor between the 

 electrodes which is the most conducting. In some cases 

 this vapor comes largely from the anode, in others from 

 the cathode. In the carbon arc where the anode is the 

 hotter the anode sends more conducting vapor into the arc 

 than the cathode does. In Steinmetz' arc between a 

 copper anode and a magnetite cathode the copper is com- 

 paratively cold and sends no vapor into the arc, while the 

 cathode sends into it vapor that is highly conducting. 



Variations of the Cathode Drop. There has thus been 

 outlined a theory of the arc as applied to the simplest form; 

 namely, the arc between two electrodes which are alike, 

 and where the gas of the arc comes from the electrodes. 

 An example of this is the mercury arc in which both elec- 

 trodes are mercury and the gas is mercury vapor. But this 

 form is exceptional in its simplicity. With the majority of 

 arcs there is a combination of gases to be considered and 

 a chance for chemical action which may modify to a large 

 extent the electrical conditions. An example of this is the 

 open carbon arc where oxidation continually occurs. 



1 Trans. Intern. Elec. Cong., St. Louis, 2, 711; 1904. 



2 Trans. Intern. Elec. Cong., St. Louis* 2, 750; 1904. 



